1. Field of the Invention
This invention relates to a two-stage expansion/collapse control mechanism for use on a hand-trailable luggage case having an auxiliary wheel unit for the purpose of controlling the expansion/collapse of the auxiliary wheel unit.
2. Description of Related Art
A hand-trailable luggage case is widely used by travelers at airports to carry personal belongings, which is equipped with wheels and an extendable handle that allows the user to easily and effortlessly carry the luggage case by dragging it on its wheels along the ground. The extendable handle is normally retracted and locked in the luggage case and can be unlocked to be extended out for the user to drag the wheeled luggage case along the ground.
Conventional hand-trailable luggage cases are typically provided with only two wheels on the bottom. This type of hand-trailable luggage case, however, is inconvenient to use since the hand-trailable luggage case would not stand by itself on two wheels. Moreover, the inclination of the luggage case would cause part of the weight of the luggage case to be transferred to the user's dragging hand, thus requiring the user to use more effort to drag the hand-trailable luggage case. As a solution to this problem, newer types of hand-trailable luggage cases are provided with an auxiliary wheel unit consisting of two swiveling wheels in addition to the main wheel unit. The auxiliary wheel unit is normally collapsed to the luggage case, and can be expanded to serve an additional wheel unit that allows the hand-trailable luggage case to stand by itself on four wheels.
One such hand-trailable luggage case is shown in FIG. 7. As shown, the hand-trailable luggage case A includes an extendable handle B, a main wheel unit C, and an auxiliary wheel unit D. The auxiliary wheel unit D includes a hinge D1, an expandable frame D2, two wheels D3 (only one is shown), and a bendable arm D4. When not in use, the auxiliary wheel unit D is collapsed into the luggage case to facilitate convenient storage. To allow the hand-trailable luggage case to stand by itself on four wheels, the auxiliary wheel unit D can be expanded to allow the luggage case to stand by itself on four wheels. Moreover, the auxiliary wheel unit can take on part of the weight of the luggage case resulted from the inclination of the luggage case, thus allowing the user to drag the luggage case with less effort along the way.
One drawback to this hand-trailable luggage case, however, is that the expansion and collapsing of the auxiliary wheel unit needs to be done by hand. When doing this, the user's hand may be hurt by the expandable frame if care is not taken. There exists, therefore, a need for a new mechanism that allows the auxiliary wheel unit to be automatically expanded out of the luggage case when the handle is being extended for use, and thereafter be automatically collapsed into the luggage case when the handle is being retracted for storage.